使用graphicsmagick在collectionFS中出现意外的空写入流

Question

我正在使用CollectionFS来管理图像.此外,我正在使用graphicsmagick gm()来处理图像.

现在我想要裁剪已保存的图像.因此,在单击事件上调用服务器方法,该方法执行crop().但是在这样做之后,我在集合中找到了一个size=0在正确日期更新的空图像.

我没有看到,我做错了什么.

shared.js

Images = new FS.Collection("images", {
    stores: [
        new FS.Store.FileSystem("thumbnail", { 
            transformWrite: function(fileObj, readStream, writeStream) {
                gm(readStream, fileObj.name()).autoOrient().resize('96', '96' + '^').gravity('Center').extent('96', '96').stream().pipe(writeStream);
            } 
        }),
        new FS.Store.FileSystem("public"),
    ]
});

server.js

Meteor.methods({
    'crop': function (fileId, selection) {
        var file = Images.findOne({ _id: fileId }),
            read = file.createReadStream('public'),
            write = file.createWriteStream('public');

        gm(read)
            .crop(selection.width, selection.height, selection.left, selection.top)
        .stream()
        .pipe(write);
    }
});

client.js

Template.editor.events({
    'click #crop': function () { 
        var fileId      = '123456789',
            selection   = { height: 100, width: 100, top: 10, left: 10 }; 

        Meteor.call('crop', fileId, selection);
    }
});

更新

正如Christian所建议的那样,我正在为writeStream使用tmp文件,因为writeStream不能像readStream一样 - 这导致了空结果.

但在写入tmp文件后,必须将其内容复制回公共存储.我怎么做？

Meteor.methods({
    'crop': function (fileId, selection) {

        var fs   = Meteor.npmRequire('fs'),
            file = Images.findOne({ _id: fileId }),
            read = file.createReadStream('public'),
            filename = '/tmp/gm_' + Date.now(),
            tmp  = fs.createWriteStream(filename);

        gm(read)
            .crop(selection.width, selection.height, selection.left, selection.top)
        .stream()
        .pipe(tmp);

        // After writing to tmp -> copy back to stream and delete tmp-file
    }
});

更新2 我试过这个:

// Add temp store
new FS.Store.FileSystem("temp")

// Method
Meteor.methods({
    'crop': function (fileId, selection) {
        var file  = Images.findOne({ _id: fileId }),
            read  = file.createReadStream('public'),
            temp  = file.createWriteStream('temp');

        gm(read)
            .crop(selection.width, selection.height, selection.left, selection.top)
        .stream()
        .pipe(tmp)
        .on('end', function () {
            var tmpread  = file.createReadStream('temp'),
                write    = file.createWriteStream('public');

            gm(tmpread).stream().pipe(write);
        });

    }
});

Answer 1

您无法读取和写入同一个文件。这相当于类似的事情

cat test | grep 1 > test

在外壳上。你可以尝试一下，test然后就会看到它是空的。

您需要在您的crop方法中创建一个中间临时文件。

假设这确实是问题所在，那么这是执行此操作的一种方法（未经测试）：

var fs = Meteor.npmRequire('fs');
var file = Images.findOne({ _id: fileId }),
var read = file.createReadStream('public'),
var filename = '/tmp/gm_' + Date.now();
var tmp = fs.createWriteStream(filename);

var gmread = gm(read)
    .crop(selection.width, selection.height, selection.left, selection.top)
    .stream();

gmread.on('end', function() {
    // done streaming through GM, copy the result back:
    var tmpread = fs.createReadStream(filename);
    var write = file.createWriteStream('public');
    tmpread.pipe(write);
});

gmread.pipe(tmp);